Korea is beefing up security ahead of next week’s visit by Pope Francis, as it prepares to escort the Catholic leader while tens of thousands of people are expected to tail his every move.

But the pope’s insistence on keeping the distance between him and ordinary people as small as possible will prove challenging for security officials.

Despite being one of the most high-profile religious leaders in the world, the famously frugal pope has rejected the use of a bulletproof car, opting instead for a humble 1600cc Kia Soul. He also turned down a proposal to wear a bulletproof vest.

Officials are especially concerned over a special Mass to be held in Gwanghwamun Square, central Seoul, next Saturday, where the pope will beatify more than 100 Korean martyrs. Up to 1 million believers and onlookers are expected to be present in one of the busiest and most heavily populated areas in Korea.

To make matters worse, the pope’s motorcade will pass by a string of high-rise buildings that will provide full view of him.

“Out of all the high-profile visitors to have come to Korea in recent years, I don’t think there has been anyone who was this much exposed (to the public),” said an official from the National Police Agency.

Police appear determined not to repeat another security fiasco like that of 1984, when a 23-year-old college student fired a toy gun at the convoy of Pope John Paul II during his visit to Korea. Although no one was injured and the “assailant” ― who was reportedly mentally unstable ― was immediately overpowered, it hinted at the chilling possibility that the pope could have been killed or injured despite the elaborate security detail.

In order to prevent possible attacks, the NPA will seal all surrounding buildings from late Friday until the end of the Mass. Police officers will be deployed on each floor of the high-rise buildings and snipers will be placed on the roofs.

A security cordon composed of a plastic wall spanning 4,500 meters will be set up around Gwanghwamun Square. Only 200,000 preregistered Catholics and government officials will be allowed to pass through metal detectors into the square to participate in the mass.

In addition, a nationwide level-1 alert ― the highest alert status for police ― will be declared throughout the visit. The alert is usually declared during emergencies or national events.

In spite of all the precautionary measures, one factor remains unaccounted for: the Argentine pontiff himself.

During his visit to Brazil last year, the pope took an unscheduled detour from the predetermined safe route after his driver took a wrong turn. Unfazed by the surrounding mob, he calmly interacted with the welcoming citizens through an open window.

While the scene shows the humility of the Catholic leader, it kept security officials on the edge of their seats.

Franca Giansoldati, a Vatican watcher who accompanied Pope Francis, told the media that the security issue was “a nightmare for everyone.”

“We will be mindful of possibilities (of the pope acting unexpectedly), because such incidents have occurred in the past during his visits to other countries,” an official from the National Police Agency said. “Of course, the fact that we’ll be prepared doesn’t mean we’ll be able to prevent them, but we will be ready.”